1. Field of the Invention
The present invention relates to a process for the production of carboxylic acids and, more particularly, to a process for the production of carboxylic acids which are less in content of impurities such as sulfur compounds and unlikely to be esterifiable.
2. Description of Related Art
Esters of tertiary carboxylic acids are widely used as ingredient for coating compositions, solvents, and the like. Esters of tertiary carboxylic acids to be used therefor are required to be high in a resistance to hydrolysis because they are exposed to severe conditions for a long period of time.
It is known that the carboxylic acid mixture mainly composed of the tertiary carboxylic acids used for the production of tertiary acid esters for the above uses is prepared by a so-called Koch's reaction.
This Koch's reaction involves reacting an olefin or an alcohol with carbon monoxide and water in the presence of an acid catalyst containing hydrochloric acid, sulfuric acid, phosphoric acid or boron trifluoride to produce a carboxylic acid having carbon atoms more than the olefin or alcohol used as a starting material by one carbon atom.
Processes for the production of tertiary carboxylic acids include the following various processes.
For example, Japanese Patent Unexamined Publication (laid-open) No. 35,048/73 has proposed a process for the production of a branched-chain carboxylic acid which is characterized in that prior to distillation of a crude fatty acid obtained by removing sulfuric acid catalyst from a reaction product, or a so-called Koch's reaction product, obtained by the reaction of an olefin with carbon monoxide and water in the presence of the sulfuric acid catalyst, the crude fatty acid is heated in a liquid phase at 100.degree. to 270.degree. C. together with water or water containing a small amount of an organic or inorganic acid salt.
This patent publication discloses, as examples of sulfuric acid catalysts, an aqueous sulfuric acid solution of more than about 80% by weight in concentration or concentrated sulfuric acid or mixtures of these sulfuric acids with at least one of boron trifluoride, hydrogen fluoride and phosphoric acid. However, as shown in Example 1, the process is carried out under high pressure condition of as high as 70 kg/cm.sup.2 in carbon monoxide pressure. Besides, this process gives only crude fatty acid mixtures containing 41.8% by weight of trichloroethylene, 42.3% by weight of branched C9 carboxylic acids and 6.2% by weight of C13 carboxylic acids. As a result of purification of such crude fatty acid mixtures, there was produced merely a C9 carboxylic acid mixture containing 49.4% by weight of 2,2,4,4-tetramethylpentanoic acid and 44.4% by weight of a mixture of 2,3,3-trimethyl-2-ethylbutanoic acid, 2,2-diisopropylpropanoic acid, 2,2,3,4-tetramethylpentanoic acid and 2,2,3,3-tetramethylpentanoic acid. Thus, a mixture of such tertiary carboxylic acids producing an ester unlikely to be hydrolyzable was obtained at the rate of as low as 50% or less. The similar result was obtained in Example 2.
On the other hand, Japanese Patent Examined Publication No. 3,362/55 discloses a process for the production of a carboxylic acid from an olefin and carbon monoxide in the presence of a catalyst including at least 90% sulfuric acid or anhydrous hydrogen fluoride alone or mixed with boron fluoride, which is characterized in that the reaction is first carried out in a liquid phase without adding water and then the reaction product was taken in water and treated at room temperature. This patent publication discloses, in Example 4, an example of the production of carboxylic acids mainly composed of trimethylacetic acid by introducing isobutene into an autoclave containing carbon monoxide kept at 50 atm. in the presence of 97% sulfuric acid and carrying out reaction at 6.degree. to 10.degree. C. for 4.5 hours. In other examples of the prior patent publication, there were also produced carboxylic acids which provide esters which are easily hydrolyzed. Thus, this patent publication discloses a process for the production of easily hydrolyzable carboxylic acids and does not disclose those which provide esters which cannot be easily hydrolyzed as in this invention.
Further, Japanese Patent Unexamined Publication No. 48,619/74 discloses a process for the production of a tertiary carboxylic acid which comprises subjecting an alcohol or olefin of at least 4 carbon atoms to addition reaction of carbon monoxide in the presence of copper, silver or gold alone or a mixed monovalent compound (excluding halides, cyanides and nitrate) using at least 80% sulfuric acid, hydrogen fluoride, fluorosulfuric acid, phosphoric acid or boron fluoride complex as a solvent under a carbon monoxide partial pressure of 0.1 atm. or higher and at -10.degree. C. to 70.degree. C.
However, Example 2 of this patent publication discloses an example of production of a mixture of 2,2-dimethylnonanoic acid and 2-methyl-2-ethyloctanoic acid from heptene-1 in a ratio of the former to the latter of 3 to 2 using 100% sulfuric acid as a solvent and cuprous oxide and aurous oxide as catalyst; Example 4 shows an example of production of pivalic acid from butene-1 in the yield of about 40% based on the olefin used using 88% sulfuric acid as a solvent and cuprous oxide and silver oxide as catalyst; and Example 6 shows an example of production of a 3:1 mixture of 2,2-dimethylheptanoic acid and 2-methyl-2-ethylhexanoic acid from 2-ethylhexene-1 using phosphoric acid as a solvent and a complex of boron fluoride with acetic acid and cuprous oxide as catalyst. It is to be noted, however, that all of these examples merely show the production of tertiary carboxylic acids which provide esters easily hydrolyzable.
Norihiko Yoneda et al., "Chemistry Letters", 1984, pp. 607-610 discloses carbonylation reaction of diisobutylene with carbon monoxide in BF.sub.3 -H.sub.2 O using Cu(I) carbonyl as a catalyst. According to this process for the production of carboxylic acids from diisobutylene shown in the above literature, the reaction without using a solvent gives carboxylic acids in a yield of 77% which comprises 32% of 32% of C5 carboxylic acids, 13% of C6-8 carboxylic acids, 36% of C9 carboxylic acids, and 19% of other carboxylic acids, while the reaction using a solvent such as cyclohexane or chlorobenzene produces carboxylic acids in yields of 80% to 82%, which comprises 41-44% of C5 carboxylic acids, 11-14% of C6-8 carboxylic acids, 35-36% of C9 carboxylic acids, and 9-10% of other carboxylic acids. Thus, the process disclosed in this literature is low in yields of carboxylic acids and besides produces only the products mainly composed of carboxylic acids which provide easily hydrolyzable esters.
Yoshie Souma et al., "Oil Chemistry", vol. 30, No. 5, p. 265 and Yoshie Souma, "Organic Synthetic Chemistry", vol. 41, p. 561-569, 1983, also disclose synthesis of carboxylic acids from olefins with metallic carbonyl catalysts, but the synthesis produces carboxylic acids in low yields and can provide only products mainly composed of such carboxylic acids so providing esters which are easily hydrolyzed.
Japanese Patent Examined Publication No. 16,897/73 discloses a purification process which is characterized by contacting an oxidizing agent with a crude fatty acid obtained by removing sulfuric acid catalyst from a so-called Koch's reaction product obtained by reacting an olefin with carbon monoxide and water in the presence of sulfuric acid catalyst prior to distillation of the crude fatty acid.